THE BUS left Cubao in Quezon City at 9:15 a.m. On to Bulacan. Nueva Ecija. Nueva Vizcaya. Isabela. Mercifully, there was a "comfort stop" at every province. Two, in fact, in Isabela, because of its length.

At 6 p.m. the driver advised the passengers to pull the window curtains shut, because of the possibility that some damned fool along the highway might hurl a rock at the bus.

Then followed an endless stretch of highway, lonely in the night. From the bus some trees could be seen on the right, the great plains on the left, and the lights of homes in the distance.

Finally, after 12 hours, the carabao-horned welcome arch of Cagayan, with a statue of a legendary hero at each base, wheezed by. And thus began, after seven years, a reacquaintance with this province on the northeastern tip of the archipelago, some 480 kilometers from Manila.

Cagayan is a province of valleys, lowland swamps, far-flung beaches in the north, hills, mountains (mostly denuded because of the extensive logging in the past that brought Mother Nature to her knees, metaphorically speaking), waterfalls, rivers, and, above all, caves.

In the town of Peñablanca alone, there are 300 caves, most of them unexplored. Cagayan is a spelunker's delight, or challenge.

A visit to Cagayan may take on the trappings of a pilgrimage because the province has many religious landmarks: St. Peter's Cathedral and San Jacinto Chapel in Tuguegarao; the basilica-shrine in Piat, with its miraculous icon of the Blessed Virgin; the cave-tabernacle at Callao; and Iguig's Calvary Hill.

There are other churches in Alcala, Lallo; Malaueg, Rizal; Gattaran; and Camalaniugan, which lays claim to the oldest bell in the country.

Calvary Hill, overlooking the Cagayan River-valley has the Fourteen Stations of the Cross, technicolored and bigger than life-size, scattered along rolling terrain behind the 210-year-old church.

The facade is again brick-lined (as are most churches in the province) and attractive, after clumsy renovation work in the early 1990s. The lateral walls of the church--some of the bricks are crumbling with age--resemble Paoay Church in Ilocos Norte with their graceful, curving ''flying buttresses.''

There is, however, an eyesore jutting out of the wall: an unpainted storehouse of cement. Why this was constructed there remains a mystery.

Like Our Lady of Manaoag and numerous other forms of the Virgin Mary, Our Lady of Piat has been credited with miracles down through the centuries. Of these, local historian Fr. Pio O. Morales cites only three.

In 1624, following a severe drought, the Itawes natives called upon Mary, confessed their sins and received Holy Communion, and were rewarded with rain that made it possible for the people to till their fields again. In 1738, an army captain, Jose Ramos, fell seriously ill, was given the last sacraments, but recovered a few days after he prayed to Our Lady of Piat. That same year, a storm which threatened a boat bound for Aparri stopped suddenly after the passengers prayed the rosary.

The Piat Basilica, a 40-minute drive from Tuguegarao, is located on a hill which overlooks the river. New stained-glass artworks bracket the ceiling, and interpret old as well as recent developments in connection with the shrine.

These include Mother Mary reportedly bringing peace among the warring tribes, miracles, and Pope John Paul II receiving a progress report on restoration work in the basilica during his first trip to the Philippines.

Be prepared for the manang (devout women) who will shower you with rosaries, novenas and medallions--all for sale, of course. And you can have these religious souvenirs blessed by the feet and robe of Our Lady through a stairway which leads to the back of the image.

The other attractions in Cagayan are the ''ecodestinations,'' the buzzword these days among the regional and provincial offices of the Department of Environment and Natural Resources.

''We have been instructed by top management to discover new ecodestinations,'' says regional executive director Elias R. Seraspi Jr. ''These we can develop with assistance from the Department of Tourism.''

Roberto C. Apigo, provincial environment and natural resources officer, is encouraging tourists to go to Claveria, near Ilocos Norte, less than three hours away from Tuguegarao, ''where we have a nice beach.'' The northern area is an entry point to the fabled islands of Palaui and Fuga.

Regional public affairs officer Constante P. Ancheta, cites the now-clean beaches in Aparri, where there are resorts with cottages; the El Presidente Resort in Buguey, where there are conference facilities; and Macatel Falls and Portabaga Falls in Santa Praxedes.

And in Santa Ana, another northern coastal town, an international port is being developed by the Cagayan Economic Zone Authority.

The ecological showpiece of the province, however, remains the Callao Caves National Park, also known as the Peñablanca Protected Landscape. It is only a half-hour drive from Tuguegarao.

You ascend 182 steps and then are greeted by stalactites and stalagmites. The impressive first chamber (some refer to it as the second chamber) has been converted into a church with a primeval altar, pews, embedded boulders serving as a retablo (altar backdrop) and topped by a grotto.

It is cool inside despite the sunlight streaming down from a big, natural hole in the ceiling, garlanded by vines and leaves. There are seven chambers, but the fifth and the sixth have been closed down because of the great earthquake in 1990.

Outside, down below, elongated pumpboats ferry passengers to the other side of the Pinacanauan River, where the resort's cottages and conference-seminar facilities are.

The boats, which also serve as transportation for the riverine folk (apart from hiking), are also available for a ride down the gorge. In the summer, domestic and foreign tourists flock to the area.

A feature of the Pinacanauan gorge is the Mororan (an Ybanag word meaning continuous rain showers). True to its name, the Mororan has falling streams of water even during the summer. The waters are supposed to have healing properties. As the boat glided under the Mororan, DENR driver Boyet Mangilim, who is an Ybanag native, advised me: ''Make a wish.''

Nearby, high up, is the Bat Cave, home to millions of bats. ''We monitored them,'' said forester Juana Mansiban. ''There are millions of them. Every day, from 6 p.m. to 7 p.m., they fly out of the cave to look for food. And they return at 4 a.m.''

Mangilim grimaced, saying: ''You can smell their urine.'' But technical staffer Jovencio Santos came to the defense of the flying foxes: ''Bats are environment-friendly. They eat mosquitoes and lice.''

The Pinacanauan river-valley rivals the gorge in Pagsanjan, Laguna, in beauty, with its thick vegetation on both sides, white-sand areas for picnics, limestone walls, and green waters. And the Callao Caves are still awe-inspiring even after a second visit.

If Pangasinan has its Our Lady of Manaoag and the Hundred Islands National Park, Cagayan has its Our Lady of Piat and the Callao Caves National Park.

How to get to the province? The leading bus lines which ply the route are Victory Liner and Baliwag Transit. And Philippine Airlines now flies to the capital of Tuguegarao three times a week.